1. Field of the Invention
The present invention relates to a method and apparatus for conveying flat printed products, and more particularly, to a method and apparatus for conveying flat printed products with respect to a rotary printing press.
2. State of the Art
U.S. Pat. No. 4,132,403 discloses a sheet transfer apparatus for a printing press. Sheets are moved from a supply to a continuously rotating receiver drum in a printing press by a transfer drum having at least two angularly spaced grippers. The transfer drum carrying the grippers is rotated at a relatively slow speed, and each of the grippers can be angularly displaced on the transfer drum and relative to the other gripper. Thus, each gripper is accelerated after it picks up a sheet at the pick-up station, so that when the gripper reaches a transfer station where it passes the sheet onto the receiver drum, it is moving at the same speed as the receiver drum. Thereafter, each gripper is uniformly decelerated, so that when it has returned to the pick-up station it is moving at the same speed as the sheet thereat.
U.S. Pat. No. 4,290,595 shows a rotatable advance or forward gripper drum. A continuously rotatable advance gripper drum assembly for sheet-fed rotary printing presses has an advance gripper drum and a gripper bridge movable relative to the drum. Furthermore, it includes a crank-driven linkage transmission device disposed on and rotatable with the drum and operatively connected to the gripper bridge for moving the gripper bridge.
U.S. Pat. No. 4,629,175 discloses a method and an apparatus for the stream-fed delivery of sheet products. Sheet-like products coming from a folder are first transported some distance before being caused to overlap. In order to slow down the products to cause the overlapping to take place and to arrange the products in a perfectly regular feed stream without being damaged, the products are engaged by grippers that are moved along a preferably arcuate path on a support in the course of which the products are slowed down by the grippers to the speed of a delivery belt on which the products are then deposited.
Finally, U.S. Pat. No. 4,767,112 discloses a folded copy product transfer and transport apparatus. To transport folded copy products without engaging an arm between the creased or folded sheets of a folded copy product, a sprocket chain has grippers secured thereto which have gripper arms at their remote end. The gripper elements are guided in an arcuate path at a transfer position or station, the folded copy product being pushed between a counter surface and a movable tongue of the gripper elements which then close due to the pressure of a spring. The gripper elements can open and close under the control of a cam to receive the copy products. The copy products can be transported in imbricated or shingled formation to a reception or delivery station.
Existing pinless folder designs have encountered the technical problem that a signature transfer from the cutting cylinders to a tape system involves a velocity differential between the cutting cylinders' surface and the driving surface of the tapes of the tape system. Through this velocity differential, a gap between adjacent signatures can be created. Consequently, the signatures can be transferred to a slowdown device.
To create and to maintain this gap between adjacent signatures, the tapes of the tape system must travel at higher velocity than the cutting cylinder surfaces. This results in a relative movement between the tape surfaces and the surface of the signature, until the signature is severed from the web by a transversal cut between the cutting cylinders. Consequently, the signatures are subjected to considerable mechanical stress which can result in signature damage or marking.